Update: The 2017 Budget made some changes for knowledge intensive companies.
Maximum investment into the company
A company can raise £5m in a 12 month period under EIS.
A company can raise £150k in its lifetime under SEIS.
Under EIS and SEIS collectively, a company can raise £5m in total in a 12 month period.
Maximum investment by an individual
An individual investor can invest £1m per year under EIS.
An individual investor can invest £100k per year under SEIS.
These differing caps are due to the tax reliefs under SEIS being more generous than under EIS.